Propellar question

On outboards some props are V tipped and other U tipped. Which is the better prop and what are the differences in performance if any?

 

Depends on the pressure distribution on the blade, what the designer is trying to do with the cord line, and the cavitation region. The idea is to maximize thrust while minimizing losses. There are several ways to to this, and each has something to offer. Not much to choose between shape, more important is the intended use of the wheel low/high speed to high/low load, etc.

 

Ok, it is an 85 hp Suzuki (two stroke) bolted to a 17ft cabin cruiser. The boat is mainly used for fishing and often runs about 15 - 20km to my favorite fishing spot - mostly on dams notorious for its bad temper and strong winds.

Currently a 13 3/4" x 15" pitch V tip propeller is fitted and she runs easily (1/3 throttle) at a brisk pace and quick out of the hole. Will a U shaped tip be better? The engine is fitted with optional hydro stabilizer fins on cavitation plate.

Ps: Had a 13" x 19" pitch U shaped tipped prop fitted and got on the plane in good time but could not get enough RPM and the motor was tilted up quite a bit to make reasonable headway and speed. The problem was the long pitch and not the tip shape I believe.

 

Wynand, You also might try reading this for a better understanding of changing props for better performance.

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Welcome I will try to help you as much as I can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as humanly possible, if you would prefer to not go to this much trouble there are other people who will gladly help you. My expectations are that you are willing to expend as much time and energy as I will to find a better prop for your boat.

Just copy this form to your computer and paste it into a word processing program and fill it out, then paste it into your post.

Iboats Boat and Motor Info

1. Year, make and model of boat

2. Length, width and base weight of boat, look for boat decal on back of boat

2a.What is the maximum recommended HP for your boat

3. Number of people and gallons of gas normally on boat

4. What do you use the boat for

5. Is it a Deep Vee and if so how many degrees of Deadrise

6. Year, manufacturer and model of motor

7. HP and gear ratio of motor IMPORTANT
If you don’t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor

8. Manufacturer’s recommended Wide Open Throttle (WOT) range

9. Anti-ventilation Plate height above the bottom of the transom of boat if it is an outboard in inches, use a straight edge or a board under the keel and sticking out to the anti ventilation plate for a reference, and take about 4 pictures for us to see.



10. Is it a bass boat or does it have a pad bottom

11. Does it have a hydrafoil, dolefin or trim tabs

12. Manufacturer, model, diameter, pitch, number of blades and whether SS or aluminum props.
IMPORTANT
1.
2.
3.

13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for less than $ 50
RPM ___________ Speed (GPS)___________ No. of people ____________ Gal. Gas ________

14. Are you at sea level or a higher elevation, give us the elevation in feet __________

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way by only using the control on the console, checked compression, looked at the plugs and checked spark, is the bottom of the boat clean and barnacle free, and have you checked the Tachometer against a mechanics tach, all of the foregoing could be the reason your prop is not attaining full RPM.

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop.

17. Does the prop show any damage that you can see

18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations

19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.
1. 3000 RPM
2. 3500 RPM
3. 4000 RPM
4. 4500 RPM
5. 5000 RPM
6. 5500 RPM
7. 6000 RPM

REMEMBER, The numbers I give you will be NO better than the information you give me.​

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.



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